1. Field of the Invention
The present invention relates to a Plasma Display Panel (PDP), and more particularly, to a PDP having an electromagnetic wave shielding electrode.
2. Description of the Related Art
A PDP includes a front case having a peripheral unit to define a window, an electromagnetic wave shielding filter to cover the window, a conductive filter holder fixed to a coupling boss of the front case by a screw to press the electromagnetic wave shielding filter onto the front case, a PDP on the rear of the filter holder, including a front panel and a rear panel, a chassis to support the PDP, connecting cables mounted on the rear of the chassis, connecting the PDP to a driver to drive the PDP, and a rear case to couple with the front case to form a case to the rear of the chassis. A thermal conductive sheet is interposed between the PDP and the chassis.
In an alternative type three electrode surface discharge PDP, the front panel includes a front substrate, sustaining electrode pairs including Y electrodes and X electrodes formed on the rear surface of the front substrate, a front dielectric layer to cover the sustaining electrode pairs, and a protective film to cover the front dielectric layer. Each of the Y electrodes and the X electrodes includes transparent electrodes formed of ITO and bus electrodes formed of a high conductivity metal. The bus electrodes are connected to a connecting cable located on the left and right sides of the PDP.
The rear panel includes a rear substrate, address electrodes crossing the sustaining electrode pairs on the front surface of the rear substrate, a rear dielectric layer to cover the address electrodes, barrier ribs to define discharge cells formed on the rear dielectric layer, and a fluorescent layer in each of the discharge cells. The address electrodes are connected to connecting cables located in the upper and lower parts of the PDP.
The electromagnetic wave shielding filter includes a central unit facing the window, and a peripheral unit surrounding the central unit. A conductive mesh layer to shield electromagnetic waves is formed in the central unit, and a metal layer to electrically connect the conductive mesh layer to the conductive filter holder is formed in the peripheral unit. The conductive mesh layer is formed on a transparent substrate and covered by a planarized layer, and a near infrared shielding layer is formed on the planarized layer. Electromagnetic energy trapped by the conductive mesh layer is transferred to the rear of the PDP via the metal layer and the conductive filter holder or discharged to the outside of the PDP.
However, the above plasma display device has a low brightness problem due to the absorption of visible light emitted from the fluorescent layer in the discharge cells, by the sustaining electrode pairs that cause the discharge, the front dielectric layer, and the protective layer on the rear surface of the front substrate through which the light must pass, and the electromagnetic wave shielding filter that has low transmission of light in front of the rear panel.
Also, in the PDP, all of the sustaining electrode pairs except the bus electrodes have to be formed of ITO electrodes, which have a high resistance, to transmit the visible light generated by the discharge cells, since the sustaining electrode pairs that cause the discharge are located on the rear surface of the front substrate, thereby increasing driving voltage. Also, the voltage drop of the ITO electrodes can cause non-uniform images in a large panel.
Also, in the PDP, the discharge occurs at the rear of the protective film in the discharge cells, since the electrodes that cause the discharge are formed on the rear surface of the front substrate through which the visible light is transmitted. This causes a drop in light emitting efficiency. Also, there is a problem of a permanent latent image due to ion sputtering on the fluorescent layer by charged particles of the discharge gas.
Also, a plasma display device having above structure is expensive to manufacture, since the electromagnetic wave shielding filter and the filter holder must be manufactured separately and then attached to the front case.
Also, in a plasma display device having above structure, a space is formed between the electromagnetic wave shielding filter and the PDP due to the thickness of the conductive filter holder. Heat generated by the PDP builds up in this space, because air circulation is blocked by the conductive filter holder. Paths for ventilation can be formed by modifying the shape of the conductive filter holder, but since the gap (the thickness of the conductive filter holder) between the electromagnetic wave shielding filter and the PDP is very small, it is difficult to provide sufficient heat discharge by air circulation.
Also, the conductive mesh layer reduces light transmission and brightness ratio by absorbing or diffracting a portion of the visible light generated by the discharge cells, since the electromagnetic wave shielding filter in front of the PDP includes the conductive mesh layer.
Also, the contrast ratio of the PDP is lowered since the PDP does not include a device for absorbing external light. Accordingly, a clear image can not be displayed. To solve these problems, an additional device for absorbing the external light can be applied to the PDP, but this requires an additional process and cost.